LONDON, U.K. - After revelations made about claims that staff at Oxfam used prostitutes - the deputy chief executive of the British charity has resigned.

Oxfam's deputy chief executive Penny Lawrence said in a statement on Monday that she was resigning over the handling of a sex scandal involving aid workers.

Oxfam has been accused of concealing the findings of an inquiry into claims staff used prostitutes while delivering aid in Haiti in 2011.

In her statement announcing her resignation, Lawrence said she was "ashamed" and takes full responsibility.

Lawrence joined Oxfam GB in 2006 as international programmes director.

According to the charity's website at the time, she was leading teams across 60 countries.

She said in a statement, "Concerns were raised about the behaviour of staff in Chad as well as Haiti that we failed to adequately act upon. It is now clear that these allegations - involving the use of prostitutes and which related to the behaviour of both the country director and members of his team in Chad - were raised before he moved to Haiti."

On Friday, a report in The Times revealed the allegation which said Oxfam's country director for Haiti, Roland van Hauwermeiren, used prostitutes at a villa rented for him by Oxfam in the aftermath of the 2010 earthquake.

The paper alleged that Oxfam knew about concerns over the conduct of Hauwermeiren and another man when they worked in Chad before they were given senior roles in Haiti.

Oxfam said allegations that underage girls may have been involved were unproven.

However, the Charity Commission launched a statutory inquiry into Oxfam - which denies a cover-up.

However, details of its scope have not yet been released.

The watchdog has reportedly said that it has concerns the charity may not have "fully and frankly" disclosed everything it knew about the claims.

The director of investigations at the commission, Michelle Russell said that if details had been known it would have dealt with the situation "very differently.”

In another statement, Mark Goldring, chief executive of Oxfam GB, admitted the charity had failed to act on complaints.

He highlighted the failure to allow Hauwermeiren to move onto another post after allegations were revealed.

Adding that the use of prostitutes was "not explicitly contrary" to Oxfam's code of conduct at the time.

Goldring added, "There was an exploration of how should the organisation respond but we didn't act on it."

Now, the European Commission is seeking full clarity and maximum transparency from Oxfam on the issue.

It warned that it is ready to "cease funding any partner not living up to high ethical standards.”